1. Field of the Invention
This invention relates to a signal detecting method in autoradiography.
2. Description of the Prior Art
Autoradiography has been known as a method for obtaining locational information on radioactively labeled substances distributed in at least one-dimensional direction to form a row or rows on a support medium.
For instance, the autoradiography comprises steps of: labeling organism-originating biopolymers such as proteins or nucleic acids with a radioactive element; resolving the radioactively labeled biopolymers, derivatives thereof, or cleavage products thereof (referred to hereafter as "radioactively labeled substances") on a gel support (support medium) through a resolving process such as electrophoresis to form a resolved pattern of the radioactively labeled substances (the resolved pattern is not visible); placing said gel support and a high-sensitivity type X-ray film together in layers for a certain period of time to expose said film and developing said film to give the autoradiograph of the resolved pattern as a visible image on the film; and obtaining the locational information on the radioactively labeled substances from said visible image. Further, the identification of the polymeric substances, determination of molecular weight of the polymeric substances and isolation of the polymeric substances can be performed based on the obtained locational information. The autoradiography has been effectively utilized for determining the base sequence of nucleic acids such as DNA.
Instead of the conventional radiography using a radiographic film which is utilized in the above-mentioned autoradiography, an autoradiographic process which utilizes a radiation image recording and reproducing method using a stimulable phosphor sheet is described in Japanese Patent Application No. 57(1982)-193418 (the content of which is disclosed in U.S. patent application Ser. No. 549,417, now abandoned, and European patent application No. 83110984.8).
The radiation image recording and reproducing method comprises steps of: placing a sample on a stimulable phosphor sheet to cause the stimulable phosphor sheet to absorb radiation energy having radiated from the sample; scanning the stimulable phosphor sheet with an electromagnetic wave such as visible light or infrared rays (hereinafter referred to as "stimulating rays") to sequentially release the radiation energy stored in the stimulable phosphor sheet as emission (stimulated emission); photoelectrically detecting the emitted light to give an electric signal; and converting the electric signal to a digital signal through A/D conversion.
The stimulable phosphor sheet used for the radiation image recording and reproducing method contains a stimulable phosphor such as a divalent europium activated alkaline earth metal fluorohalide phosphor. When exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, or ultraviolet rays, the stimulable phosphor stores a portion of the radiation energy and then emits light corresponding to the radiation energy stored therein upon excitation with an electromagnetic wave (stimulating rays) such as visible light or infrared rays after exposure to the radiation.
The autoradiography utilizing the above-mentioned radiation image recording and reproducing method is free from various limitations on the measuring conditions which are required in the autoradiography utilizing the conventional radiography, and accordingly the autoradiographic process can be noticeably simplified. Further, the locational information on the radioactively labeled substances can be obtained as an electric signal and/or digital signal without visualizing an autoradiograph having the locational information thereof, so that it is possible to improve the accuracy of determination of the locational information and to increase the amount of the information.
A digital signal processing method for obtaining information on one-dimensional location of radioactively labeled substances in the form of symbol and/or numeral in the autoradiography utilizing the radiation image recording and reproducing method is described, for instance, in Japanese Patent Application No. 58(1983)-1326 (the content of which is disclosed in U.S. patent application Ser. No. 568,877, now abandoned, and European patent application No. 84100144.9). Said signal processing method comprises steps of: determining a one-dimensional scanning line (namely one-dimensional distribution direction of the radioactively labeled substances) for signal processing with respect to the obtained digital signal; and detecting sampling points on the scanning line. The term "scanning" in this method means the numeral scanning on the digital image data.
According to the above-mentioned signal processing method, the information on one-dimensional location of the radioactively labeled substances, which has been relied on the visual judgment of investigators in the conventional art, can be obtained automatically and accurately in the desired form such as symbol and/or numeral. Consequently, the signal processing method brings about an improvement of the accuracy of locational information and increase of the amount of information.
Another signal processing method in the autoradiography utilizing the radiation image recording and reproducing method, which comprises determining the scanning line for detecting sampling points with respect to the obtained digital signal, is described in Japanese patent application No. 58(1983)-1328 (the content of which is disclosed in U.S. patent application Ser. No. 568,906 and European patent application No. 84100150.6).
In any signal processing method described above, the one-dimensional distribution direction (scanning line on the digital image data for detecting sampling points) of the radioactively labeled substances is determined, after the digital signal corresponding to the autoradiograph having the locational information on the radioactively labeled substances is obtained by photoelectrically detecting (reading out) the stimulable phosphor sheet on which the autoradiograph is recorded. Therefore, the obtained digital signal is initially stored in a memory of a signal processing circuit and subsequently the digital signal are selectively taken out of the memory according to the signal processing operation, so as to determine the one-dimensional distribution direction of the radioactively labeled substances.
More in detail, the read-out of the stimulable phosphor sheet is carried out over its entire surface and the digital image data are inevitably obtained even on an vacant area of th sheet which does not give any locational information on the radioactively labeled substances. That is, all of the digital signal which is obtained by detecting on the entire surface of the stimulable phosphor sheet should be temporarily stored in the memory of the signal processing circuit, and thus the memory requires a great capacity for storing it.
Additionally, the photoelectrical read-out operation on the stimulable phosphor sheet requires not a short period of time, because the operation should be carried out over the entire surface thereof.